Study Finds Firstborn Children More Prone to Allergies

A recent study conducted by Taiwanese researchers reveals that firstborn children are more likely to develop allergies and asthma compared to their younger siblings. This research, published in September 2023 in the journal Pediatric Allergy and Immunology, highlights a potential link between Taiwan’s declining birthrate and the increasing prevalence of allergic conditions among children.

The study analyzed data from the Taiwan Birth Registration Database between 2004 and 2014 and connected it to the National Health Insurance Research Database. Researchers categorized children based on their birth order to assess the relationship between birth order and the risk of allergies. Over the years, Taiwan’s fertility rates have seen a significant decline, dropping from 3.69 in 1970 to 0.87 in 2023. During this same period, the prevalence of asthma among children surged from 1.3 percent in 1974 to 20.3 percent in 2019. Rates of allergic rhinitis, or hay fever, increased from 7.8 percent to 50.6 percent, while eczema cases rose from 1.4 percent to 11.3 percent.

The findings indicated a clear trend: children born later in the family hierarchy face a lower risk of developing allergies. Specifically, the study found that second-born children had a 21.3 percent lower risk of eczema, while third-born and later children saw a reduction of 37.5 percent. In terms of asthma, second-borns had a 25.0 percent reduced risk, with third-borns experiencing a 26.9 percent reduction. For hay fever, the figures stood at 16.3 percent for second-borns and 29.3 percent for those born third or later.

The authors of the study, Chan Chin-kan, a pediatrician at Taoyuan General Hospital, and Chen Pau-chung, director of the National Institute of Environmental Health Sciences, suggest that these patterns might stem from “reduced microbial exposure earlier in life” for firstborns. They did not delve into the specifics of why firstborns might be at a higher risk, but the implications of smaller family sizes are evident.

Taiwan has witnessed a dramatic shift in its demographics, with the fertility rate plummeting over the decades. In 1998, the fertility rate was 1.5, and now it stands at less than 1.0, contributing to concerns over an aging population. The rise in allergic diseases coincides with these changes, prompting researchers to explore the interplay between family size and health outcomes.

As Taiwan navigates its demographic challenges, the implications of this study could lead to a deeper understanding of how early life exposures shape health trajectories. The findings not only shed light on the health of children but also raise questions about the broader societal shifts linked to declining birth rates.